Since the role of the right-handed hitter would be to perform well against southpaw pitchers, let’s take a look at just how good each hitter performs in that match-up going by weighted on-base average (wOBA), my preferred metric for analyzing offensive production.

Click the chart below to view a larger version.

An average wOBA is equal to the league average on-base percentage. Last year excepting, that OBP has been around .330 to .335. So all ten hitters are above-average when facing LHP, but only four have been elite hitters against them. Jeff Francoeur is the worst realistic option — no surprise there — while post-season pest Cody Ross and Phillie-killer Matt Diaz are among the best.

Going by only 2010 performance, we see that the two Nationals and two Twins — Morse, Willingham, Young, and Cuddyer — performed better than their career averages while Hairston and Rowand notably under-performed. Francoeur stayed right around his career average, which is nothing to write home about.

As mentioned in this article, the Phillies should be aiming to minimize variance. Players like Morse and Young both hit very well against lefties in 2010, but well above what they had traditionally hit against lefties over their careers. While they certainly could have made some adjustments at the plate, which would explain the better performance, it is still very likely that their production regresses to the mean. The Phillies would then be paying essentially for 2010-level production when they should be expecting something smaller.

Thus, it seems that among the ten candidates, Willingham is the best option with Ross a close runner-up. Both have had very consistent production against lefties over the last three years and that production has always been elite.

If GM Ruben Amaro decides that the price tags on those two outfielders are too hefty, he can fall back on a reliable in-house option by the name of Ben Francisco. He has a career .352 wOBA against lefties over his career and hit .384 against them last year. Francisco is arbitration eligible for the first time, meaning he’s cost controlled through 2013. If the Phillies give Francisco enough playing time between now and then, and he emerges into a productive player, they could potentially earn some draft pick compensation if and when he leaves for free agency whereas players like Francoeur and Rowand would not provide that benefit.

When it comes to filling this roster spot, Amaro needs to swing for the fences or go home. Go get Willingham or Ross, or be happy with a very affordable and familiar face in Francisco.